Capacitor



May 23, l93 9 G. GRUNDMANN CAPAC ITO R Filed Jan. 5, 1938 lnvemolGustave L. Grundmann Egg dttorneg Patented May 23, 1939 UNlTso STATESUAPCITR tion of Delaware Application January 5, 1938, Serial No. 133,@1

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This inventionv relates to capacitors and has special reference to theprovision of improvements in fixed capacitors of a value of capacitancecapable of being utilized in so-called "micro-wave and ultra-highfrequency signaling systems.

The capacitorsusually employed in high frequency work comprise one ormore elemental capacitors constituted of alternate metal and dielectriclayers. Such capacitors, as heretofore constructed, are objectionable inthat the current path through the assembly is longer than need be, sothat unwanted inductance is introduced into the capacitorl The added orspurious inductance of a capacitor may be so great as to seriously alterthe impedance of the circuit in which it is connected, especially so ifthe cir- Cuit is designed to transmit electrical waves of but a fewcentimeters in wave-length.

Accordingly, the principal object of the present invention is to providea fixed capacitor having an extremely low effective inductance rating.

Another object of the invention is to provirr a simple, inexpensive andtrouble-free by-pass 25 capacitor and one which may be readily attachedas to the chassis of radio set. v

Other objects and advantages together with certain details ofconstruction will be apparent and the invention itself will be bestunderstood.

30 by reference to the following specification and to the accompanyingdrawing, wherein Figure l is a longitudinal sectional view,

Figure 2 is a plan view,

Figure 3 is an exploded view of an elemental 35 capacitor constructed inaccordance with the principle of the invention,

Figure 4 is a longitudinal sectional view, and

Figure 5 a plan view of a capacitor of modified construction.

l? Like reference characters represent the same or corresponding partsin all figures.

The elemental capacitor of Figs. 1, 2 and 3 comprises two metalarmatures or electrodes I and 3. respectively, an interposed dielectriclayer or plate 2 and an insulating disc or washer 4 superimposed uponthat surface of electrode 3 which is opposite to that contiguous thedielectric plate 2. The electrodes I and 3 may be constituted of brassor other suitable metal; each 50 has a substantially flat, preferablycircular, electrode surface Ia, 3a respectively. Electrode I is providedwith an upstanding wall or rim Ib whose inner surface forms a rightangle continuation of the fiat electrode surface Ia. The interposeddielectric layer 2 may be constituted of (ill. TIS-41) mica, sheeted orsprayed styrol (or the polymerization products thereof) or othersuitable dielectric material. The diameter of the dielectric layer 2 andof the insulating washer 4 corresponds substantially to that of theinternal diameter of the cup-shape electrode l, so that they v may besnug-fitted therein, The diameter of electrode 3 is somewhat less thanthe internal diameter of electrode I it is adapted to be maintained outof short-crcuiting contact with the rim Ib, by the insulating washer 4,which is superimposed upon the outwardly facing surface of electrode 3.In assembling the capacitor of Figs. l, 2 and 3, the dielectric materialis first applied to, or fitted snugly against, the electrode surface laof the cup-shape electrode I; the electrode 3 of smaller diameter isplaced contiguous the opposite surface of layer 2, the insulating washeris then iitted within the cup on top of the electrode 3 and finally theprotruding rim of the upstanding wall Ib of electrode I is rolled,crimped, or otherwise bent inwardly so that only a narrow edge portionIc contacts the exposed outer surface of the washer 4. With the partsthus assembled, electrode 3 is malntained in spaced insulating alignmentwith respect to the cup-shape electrode I by the clamping force appliedto the outer surface of the washer 4.

As previously pointed out, the present invention contemplates anelemental capacitor characterized by its extremely low effectiveinductance rating. This desired characteristic is achieved in accordancewith the invention by connecting the necessary electrode leads to themid-points of the electrode plates, so that a radial electron or currentpath is established through the electrodes which is substantially nolonger than the radius of the larger electrode I. The current path, andhence the effective inductance of the capacitor of the present inventionis thus reduced by at least one-half as compared with prior artcapacitors wherein the electrode leads are affixed to diametricallyopposite points on the edges of the electrodes. As compared withcapacitors wherein the electrode leads are affixed to adjacent points onthe electrodes, the capacitors of the present invention provide an evengreater reduction in inductance rating.

The electrode leads, here designated II and I3, are preferably integralwith the electrodes I and 3 to which they are respectively connected.One or both of the leads are preferably screw-threaded as indicated at II a, so that it may be received in a complementary threaded orifice in ametal chassis or plate (not shown) when the capacitor is employed as aby-pass for radio frequency currents. Alternatively, the threads lla maybe omitted and the projecting connector I I riveted or otherwise axed tothe chassis.

The capacitor of Fig. 4 is similar in all of its essential parts to thecapacitor of Figs. 1 to 3, inclusive; its capacitive rating however isisomewhat higher. The higher capacitive rating is achieved without anyincrease in overall dimensions by extending the turned in rim Ic of thecup-shape electrode i beyond the periphery of the smaller electrode 3.

Other modications of the invention will suggest themselves to thoseskilled in the art. It is to be understood, therefore, that theforegoing is to be interpreted as illustrative and not in a limitingsense, except as required by the prior art and the spirit of theappended claims.

What is claimed is:

1. A capacitar comprising a pair of electrode plates of unequaldiameter, an interposed dielectric layer, a pair of electrode leadsconnected respectively to points substantially in the center of theoutwardly facing surfaces of said plates, an insulating washersuperimposed on the plate of smaller diameter and through which its leadextends, and an inwardly turned rim on the plate of larger diameter `forexerting a clamping force upon said insulating washer.

2. The invention as set forth in claim 1 wherein said inwardly turnedrim extends inwardly beyond the periphery of the smaller of saidelectrode plates.

GUSTAVE L. GRUNDMANN.

